Wastewater is generated from a variety of municipal, commercial, and industrial sources. Prior to environmental regulations, wastewater was discharged into waterways and landfills. Wastewater sludge, also generated at a wastewater treatment facility, may undergo additional treatment.
Wastewater treatment facilities are treating the wastewater sludge to produce biogas and biosolids from anaerobic digestion, a naturally-occurring process. The biogas generated includes a blend of methane and carbon dioxide gas that may be used as fuel, and biosolids generated from the anaerobic digestion are nutrient-rich organic materials that may be used as fertilizers. The anaerobic digestion process occurs in three phases: hydrolysis, fermentation, and biogas formation.
Although naturally-occurring, biological materials may be more easily degraded than others. To increase biological degradation of the wastewater sludge to form a hydrolyzed sludge, thermal hydrolysis may be used as the first step of anaerobic digestion, where thermal hydrolysis is a two-stage process that combines pressure cooking and rapid decompression. As a result of thermal hydrolysis, hydrolyzed sludge is more biodegradable, which results in a greater production of biogas and biosolids.
Processes for improving the yield of biogas and reducing volatile solids in biosolids sludge are needed in addition to other improvements, such as thermal hydrolysis. The processes disclosed herein achieve desired enhancement of biosolids sludge treatment.